Bobbin for a sewing machine



March 30, 1965 s. J. KETTERER 3,175,783

BOBBIN FOR A SEWING MACHINE Filed NOV. 13, 1962 |4- I AE Fig.3

INVENTOR.

' Skmley J. Kefferer WITNESS ATTORNEY 3,l75,783 Patented Mar. 30, 1965 3,175,783 BOBBM FOR A SSEWENG MACEHNE Stanley J. Ketterer, Morris Plains, NJ assignor to The Singer Company, a corporation of New Jersey Fiied Nov. 13, 1962, Ser. No. 236,797 4 Claims. (Cl. 242118.4)

This invention relates to thread carrying bobbins for lock stitch sewing machines, and more particularly to a bobbin adapted for use with a lock stitch forming mechanism of the type in which resistance to turning of the bobbin is applied in order to develop the requisite tension in the bobbin thread for satisfactory stitch setting.

There are several advantages which accrue from the use of an arrangement in which the bobbin thread is tensioned by the application of frictional resistance to turning of the bobbin as compared with the use of a thread tensioning spring or the like disassociated with the bobbin and acting directly on the bobbin thread. These advantages include simplicity of construction, ease of bobbin thread replenishment or exchange of bobbins in a machine, and absence of tension variations resulting from surface characteristics of the thread. There has however, been one serious disadvantage to an arrangement in which resistance is applied to the turning of the bobbin in that when a conventional bobbin is used, there arises a noticeable gradient of tension applied to the bobbin thread increasing from a full to an empty bobbin.

To overcome the frictional resistance to turning of the bobbin, the thread when fully wound on the bobbin acts at a relatively large lever arm distance and, consequently, the force generated as tension in the thread is less than when the bobbin is nearly empty and the threads act on a relatively small lever arm distance.

It is an object of this invention to provide a bobbin for a sewing machine adapted for use in an arrangement in which frictional resistance to turning of the bobbin is applied in order to develop tension in the bobbin thread and in which the force generated as tension in the bobbin thread is substantially uniform from a full to an empty bobbin. By substantially uniform is meant such degree of uniformity as will escape detection of variation in the appearance of the resulting lock stitches.

It is an object of this invention to provide a composite sewing machine bobbin comprising an inner reel journaled within an outer reel with the rotation of the outer reel being fricitonally resisted relatively to the sewing machine stitch forming instrumentalities and the rotation of the inner reel being frictionally resisted relatively to the outer reel. The bobbn thread when fully wound on the bobbin will lock the inner and outer reels together, the thread when unwound to a point intermediate full and empty vtn'll unlock the reels and permit relative rotation therebetween so as to obviate the thread tension gradient which usually exists.

Most bearing arrangements between the inner and outer reels of a composite bobbin of this invention would give rise to an abrupt change in the thread tension when the thread unwound to the intermediate point at which the inner reel becomes unlocked from the outer reel. An abrupt revision of the frictional forces, even if of only a small difference in magnitude, would result in a noticeable change of appearance in the stitches being formed.

It is a further object of this invention to provide a unique bearing arrangement between the inner and outer reels of a composite sewing machine bobbin, effective when the bobbin reels are unlocked, to provide a gradual transition of the frictional forces and consequently more uniform tension on the thread from a full to an empty bobbin.

With the above and additional objects and advantages in view as will hereinafter appear, this invention comprises the devices, combinations and arrangements of parts hereinafter described and illustrated in the accompanying drawing of a preferred embodiment in which:

FIG. 1 represents a top plan view of a sewing machine loop taker having arranged therein a bobbin in accordance with this invention,

FIG. 2 is a cross sectional view taken substantially along line 2-2 of FIG. 1 of the loop taker and bobbin of this invention, and

FIG. 3 is an enlarged cross sectional view of the bobbin taken substantially along line 2-2 of FIG. 1 and showing thread Wound thereon.

The loop taker 11 illustrated in the accompanying drawings is of the type illustrated and described in greater detail in my co-pending United States application Serial No. 133,896, filed August 25, 1961, now Patent No. 3,115,- 855, to which reference may be had. It will be sufiicient for an understanding of this invention to appreciate that the loop taker 11 comprises a cup-shaped body portion 12 carried on a drive shaft 13 journaled in a bearing 14 in a bed portion 15 of the sewing machine frame. The rim of the cup-shaped loop taker body portion 12 is formed internally with an arcuate bearing rib 16 and the rim is split to define a needle loop seizing beak 17.

A bobbin case if: is formed with an arcuate bearing groove 19 journaled on the bearing rib 1s of the loop taker body portion. The bobbin case is also formed with a pair of abutment surfaces 20 which cooperate with bifurcated fingers 21 of a rotation restraining member 22 carried in the sewing machine bed 15 to constrain the bobbin case journaled on the loop taker bearing rib and to prevent rotation of the bobbin case with the loop taker. A leaf spring 23 may be interposed between one of the fingers 21 and the abutment surface 20 complemental thereto to cushion the slight vibration of the bobbin case occasioned by the passage of needle thread loops about the bobbin case.

The bobbin case is formed internally with a through circular opening 24 to accommodate a bobbin indicated generally as 25. The upper surface of the bobbin case adjacent to the circular opening 24 is formed with a planar shelf 26 adapted to support one flange of the bobbin. Pivoted on a pin 27 in the bobbin case is a radial arm 28 formed near the free extremity with a locating hole 29 adapted to center the bobbin in the bobbin case opening 24. The hub portion 34 of the radial arm is slabbed as at .31 and cooperates with a leaf spring 32 in the bobbin case to bias the radial arm 28 downwardly and against the bobbin so as to apply a normal force for developing friction between the bobbin and the bobbin case tending to restrain rotation of the bobbin. An adjusting screw 33 in the bobbin case may be used to vary the tension of the leaf spring 32 so as to vary the frictional resistance to turning of the bobbin relatively to the bobbin case. A depression 34 in the planar shelf 26 of the bobbin case provides for egress of thread wound on the bobbin.

Referring particularly to FIG. 3, the bobbin 25 of this invention is formed with an inner reel portion comprising a bottom flange and an intermediate flange 41 secured together by a fastening screw 42 threaded into a hub portion 43 formed on the bottom flange 40. The hub portion 43 and a hub portion 44 formed on the intermediate flange 41 are each slightly frustoconical for the purpose of leading the initial thread loops wrapped on the bobbin toward the plane of division between the hub portions. The hub portion 43 adjacent the plane of division between the hub portions is also formed with a shallow beveled edge 45 which forms a narrow thread gripping groove 45 when the hubs 43 and 44 are secured together.

The fastening screw 42 is formed with a cylindrical 3 shoulder 47 engaging the intermediate flange 4-1 and with an enlarged cylindrical head 43 surmounted by a small cylindrical pin 49 adapted to be embraced by the locating hole 29 of the radial arm 28.

Journaled on the shoulder 47 and between the intermediate flange 41 and the enlarged head 48 of the fastening screw is a dislolike flange member 5t which together with the bottom flange 40 forms the outer reel portion of the bobbin. The flange member 50 is formed with circular seat 51 embracing the intermediate flange 41 so that the inside surfaces of the flange member 50 and the intermediate flange 41 are substantially co-planar.

As illustrated in FIG. 3, the bottom flange 40 is of a diameter greater than that of the intermediate flange but less than that of the flange member 50 so that thread when fully wound on the bobbin extends between the flanges 40 and 50 and locks all of the parts together for rotation as an integral unit. As illustrated in FIG. 2, the flange member 50 rests at the periphery on the shelf 26 of the bobbin case and the frictional forces developed therebetween as a result of the normal force applied by the radial arm 28 provides the major rotation constraining influence on the bobbin, and therefore, the tension applied to the thread withdrawn from a full bobbin. The frictional forces between the radial arm and the fastening screw being applied on an exceedingly small radius will be negligible.

As the thread is unwound from the full bobbin, the tension applied as a result of the friction between the flange member 50 and the bobbin case shelf 26 will gradually increase since the lever arm distance represented by the outer diameter of thread on the bobbin will be decreasing while the lever arm distance at which the friction forces are applied remains constant. This tension increase is of such a gradient that if continued to an empty bobbin it would increase to the point at which the appearance of the resulting stitches would change.

With the bobbin of this invention, however, when the thread is consumed to the point at which the thread diameter on the bobbin equals that of the intermediate flange 41, the inner reel comprising the bottom flange 4t) and intermediate flange 41 becomes free to rotate relatively to the flange member 51 and the friction forces acting between the intermediate flange 41 and the flange member 50 begin to influence the tension applied to the thread. Since the forces between the flanges 41 and 50 are applied at a far smaller lever arm distance than are the friction forces acting between the flange 50 and the bobbin case, the thread tension influences by rotation of the inner reel alone will be reduced substantially to the level applied when the bobbin is fully wound.

In order to provide for a gradual reduction in the thread tension applied as the thread unlocks the inner reel for movement relatively to the flange member 50, it has been found that the clearance between the flange member 50 and the shouldered portion 47 of the fastening screw should be greater than the clearance between the circular seat 51 in the flange member 50 and the periphery of the intermediate flange 41.

Apparently such gradual reduction in the thread tension results from two circumstances, first, the bobbin thread of a sewing machine is drawn from the bobbin periodically and the bobbin thread tension which is of concern in sewing is that tension at or near the peak or maximum tension applied each individual time that the bobbin thread is drawn from the bobbin. Second, the friction forces which exist between the periphery of the intermediate flange 41 and the circular seat 51 are derived only in relation to the normal force therebetween, which normal forces are a function of the tension in the thread and the relation of the lever arm distances of the thread and of the circular seat 51. Insofar as concerns the thread tension, therefore, the inner reel when first unlocked utilizes the tension in the thread to generate i tension in the thread and apparently results in a momentary bobbin thread tension peak sufficiently large as to turn the flange 50 relatively to the bobbin case. T urning of the flange 50 thus serves as a safety valve limiting the peak bobbin thread tension when the inner reel is first unlocked.

As the thread is unwound from the bobbin beyond the diameter of the intermediate flange periphery, turning of the flange 5t) relatively to the bobbin case Will gradually diminish and a substantially uniform bobbin thread tension will be imposed until the bobbin is empty.

Throughout this specification the flanges 4t and 41 have been referred to collectively as the inner reel and the flanges 4t and 50 collectively as the outer reel. The flange 40 thus cooperates in both capacities, but the result would be the same if two completely separate reels were to be used, one journaled within the other with each side thereof having flanges arranged as are flanges 4i and fit of the preferred embodiment of the drawings.

Having thus set forth the nature of this invention, what I claim herein is:

l. A bobbin for a lock stitch sewing machine comprising a hub means, a pair of circular flanges extending radially from said hub means in axially spaced relation thereon, said pair of circular flanges being formed with opposed substantially parallel planar thread engaging surfaces, and an additional flange disposed contiguous to at least one of said pair of circular flanges, said additional flange being formed with a circular seat freely journaled on the periphery of said one of said pair of circular flanges and cooperating therewith to provide the sole radial constraint for said additional flange relatively to said hub means, a planar thread engaging surface formed on said additional flange radially outward beyond said contiguous one of said pair of flanges, and means for constraining said additional flange axially relatively to said bobbin with the thread engaging surface of said additional flange substantially co-planar with the thread engaging surface of said contiguous one of said pair of circular flanges during relative rotation therebetween.

2. A bobbin for a lock stitch sewing machine comprising a hub means, a pair of circular flanges having substantially planar inside surfaces of different diameters extending radially from said hub means in axially spaced relation thereon to define an inner reel, and an additional flange formed with a substantially planar inside surface and a circular bearing seat, means associated with said hub means for constraining said additional flange with said bearing seat rotatably embracing the periphery of that one of said pair of inner reel flanges having the smaller diameter and with the inside surfaces of said additional flange and of said one inner reel flange being substantially coplanar during rotation of said inner reel relatively to said additional flange, and said additional flange having a peripheral diameter greater than that one of said inner reel flanges of larger diameter and adapted to be interlocked rotationally with said inner reel flange of larger diameter by a predetermined quantity of thread wound on said bobbin.

3. A bobbin for a lock stitch sewing machine comprising a hub means, a pair of circular flanges having substantially planar thread engaging surfaces extending radially from said hub means in axially spaced relation thereon, an additional flange having a substantially planar thread engaging surface and formed with a circular bear: ing seat, fastening means acting between said additional flange and said hub means for constraining said additional flange axially of said hub means with said circular seatin journaled relation on one of said pair of circular flanges and with the thread engaging surfaces thereof substantially coplanar, the radial clearance between said additional flange and said fastening means being of such magnitude that said circular seat journaled on the periphery of said one of said pair of circular flanges pro-- vides the sole radial constraint for said additional flange relatively to said hub means.

4. A bobbin for a lock stitch sewing machine comprising a hub portion, a pair of circular flanges having substantially planar thread engaging surfaces of unequal peripheral diameter extending radially from said =hub portion, an axial stud for securing said hub portion and said pair of circular flanges for movement as a unit, an additional flange member having a substantially planar thread engaging surface of peripheral diameter at least as large as that of said one of said pair of circular flanges of larger peripheral diameter, said additional flange being formed with a clearance aperture embracing said stud and with a circular seat freely journaled on the periphery of that one of said pair of circular flanges having the smaller peripheral diameter, and means on said stud for constraining said thread engaging surface of said additional flange substantially coplanar with the thread engaging surface of the smaller of said pair of circular flanges with said circular seat providing the sole radial constraint for said additional flange member.

References Cited by the Examiner UNITED STATES PATENTS 323,916 8/85; Corey 242-125 1,187,986 6/16 Goldsmith 242-118.4 2,000,372 5/35 Beck 242-1l8,62 X 3,106,176 10/63 Doerner 112181 X MERVIN STEIN, Primary Examiner. 

2. A BOBBIN FOR A LOCK STITCH SEWING MACHINE COMPRISING A HUB MEANS, A PAIR OF CIRCULAR FLANGES HAVING SUBSTANTIALLY PLANAR INSIDE SURFACES OF DIFFERENT DIAMETERS EXTENDING RADIALLY FROM SAID HUB MEANS IN AXIALLY SPACED RELATION THEREON TO DEFINE AN INNER REEL, AND AN ADDITIONAL FLANGE FORMED WITH A SUBSTANTIALLY PLANAR INSIDE SURFACE AND A CIRCULAT BEARING SEAT, MEANS ASSOCIATED WITH SAID HUB MEANS FOR CONSTRAINING SAID ADDITIONAL FLANGE WITH SAID BEARING SEAT ROTATABLY EMBRACING THE PERIPHERY OF THAT ONE OF SAID PAIR OF INNER REEL FLANGES HAVING THE SMALLER DIAMETER AND WITH THE INSIDE SURFACES OF SAID ADDITIONAL FLANGE AND OF SAID ONE INNER REEL FLANGES BEING SUBSTANTIALLY COPLANAR DURING ROTATION OF SAID INNER REEL RELATIVELY TO SAID ADDITIONAL FLANGE, AND SAID ADDITIONAL FLANGE HAVING A PERIPHERAL DIAMETER GREATER THAN THE ONE OF SAID INNER REEL FLANGES OF LARGER DIAMETER AND ADAPTED TO BE INTERLOCKED ROTATIONALLY WITH SAID INNER REEL FLANGE OF LARGER DIAMETER BY A PREDETERMINED QUANTITY OF THREAD WOUND ON SAID BOBBIN. 